Figures REF  (a) and (b) demonstrate the effect of the addition of graphene coatings of varyious thicknesses to the Ag surface, in the case of a SiO\(_2\) /Si substrate. For up to three layers of graphene, the surface peak remains virtually unchanged. However, at three layers, the bulk peak amplitude is reduced by approximately \(50 \%\) . This effect is attributed to the introduction of a thin boundary layer, decreasing the bulk resonance amplitude. Imposition of a boundary leads to simultaneous diminished coupling to bulk modes and enhanced coupling to surface modes, physically similar to the aforementioned begrenzung effect. [1]}, [2]}, [3]} At 20 layers, as we would expect, the bulk peak broadens significantly (indicating increased losses) and the system has spectral properties (broadening and peak position) resembling those of graphite on silver. Peak positions calculated for the 20-layer graphene coating (\(\approx 2.6\,\) eV and \(\approx 3.5\,\) eV) are very close to those measured in EELS of thin films of Ag nanoparticles evaporated on graphitic surfaces, for example \(2.2\,\) eV and \(3.4\,\) eV. [4]} Differences in peak position (particularly for the lower-energy peak) are attributable to differences in morphology between the Ag slab in our calculations and the film of Ag nanoparticles in the experimental samples.
